Updates capacity settings for a fleet. Use this action to specify the number of EC2 instances (hosts) that you want this fleet to contain. Before calling this action, you may want to call DescribeEC2InstanceLimits to get the maximum capacity based on the fleet's EC2 instance type.
If you're using autoscaling (see PutScalingPolicy), you may want to specify a minimum and/or maximum capacity. If you don't provide these, autoscaling can set capacity anywhere between zero and the service limits (http://docs.aws.amazon.com/general/latest/gr/aws_service_limits.html#limits_gamelift).
To update fleet capacity, specify the fleet ID and the number of instances you want the fleet to host. If successful, Amazon GameLift starts or terminates instances so that the fleet's active instance count matches the desired instance count. You can view a fleet's current capacity information by calling DescribeFleetCapacity. If the desired instance count is higher than the instance type's limit, the "Limit Exceeded" exception occurs.